1. Field of Invention
The present invention relates to a luminance adjusting device. More particularly, the present invention relates to a luminance adjusting device for automatically adjusting luminance of a lamp unit.
2. Description of Related Art
Display is the key tool to display communication information as an image manner for viewing by people. For example, computer system or TV system need a display for displaying the image. Recently, the display technology has been greatly developed. The display mechanism for panel display, such as the liquid crystal display (LCD), is quite different from the rather conventional cathode-ray-tube (CRT) display, and has been successfully developed. The LCD device usually needs a light module, such as a backlight module, to serve as the light source, so that each image pixel can produce the desired color light, and then a full image is formed.
A conventional LCD is, for example, shown in FIG. 1. In FIG. 1, the LCD 100 includes a bezel frame 102. A displaying cell assembly 104 for displaying the image is held by the frame 102. Then, several device elements, such as a plastic frame 106, an optical film & diffuser plate 108, lamp holders 110a, 110b, a light module 112, a reflection sheet 114, and a back cover 116 are sequentially stacked behind the displaying cell assembly 104, so as to form the LCD 100. The location 118 is for signal input.
For the conventional LCD 100 in FIG. 1, the light module 112 is composed by several lamp units, such as the cold cathode fluorescent lamps (CCFLs). All of the lamp units are assembled together as an integrated light module. If one of the lamp units is damaged and needs to be changed, then it is necessary to replace the whole light module. This causes the high cost in maintenance. In order to solve this issue, another design of the light module is allowing each lamp unit to be individually control in power and therefore each the lamp unit can be individually replaced.
FIG. 2 is a drawing, schematically illustrating another LCD with the light module having several replaceable lamp units. In FIG. 2, the bezel frame 102 and the displaying cell assembly of the LCD are shown. Then, the backlight module is composed of several lamp units 200. Each lamp units 200 can be separately controlled in power and replaceable.
The design of light module in FIG. 2 still has the disadvantages. The design of FIG. 2 allows each lamp unit 200 to be replaceable, so that it is not necessary to replace the whole light module. However, since the luminance (brightness) of the lamp is usually reducing according to the total operation time of the lamp, the newly replaced lamp unit usually has the stronger luminance than the luminance of the other lamp units. This phenomenon is described in FIG. 3. In FIG. 3, when a new lamp unit 302 replaces the old lamp at the region 304 in the display area 300, the distribution of the luminance is schematically shown in the right drawing. As one can see, the luminance (Lum) at the region 304 is larger. For the actual displayed image, a brighter stripe in the display screen would appear. This non-uniform luminance causes the poor quality for the displayed image. Particularly, the defect lamp unit to be replaced usually has been operated for a long time period. In this situation, the luminance for the other old lamp units has been significantly reduced. At this moment, the luminance levels between the other old lamp units and the newly added lamp unit have been quite different. This then causes the poor image quality.
The design to solve the foregoing conventional issues is still in need by the manufacturers.